Strip loop tension control means



Dec. 24, 1968 w. G. RITTER STRIP LOOP TENSION CONTROL MEANS 2 Sheets-Sheet 1 Filed April 16, 1 3

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Attorneys 8 50 4 NE E% Dec. 24, 1968 w. G. RITYTER 3,417,585

STRIP LOOP TENSION CONTROL MEANS Filed April 16, 1963 2 Sheets-Sheet 2 INVENTOR WAYNE G. RITTER A Horneys United States Patent 3,417,585 STRIP LOOP TENSION CONTROL MEANS Wayne G. Ritter, Pittsburgh, Pa., assignor to Ritter Engineering Company, a corporation of Delaware Filed Apr. 16, 1963, Ser. No. 273,446 5 Claims. (Cl. 728) This invention relates to mill loopers and more particularly to vertical uploopers for continuous rolling mills.

In the manufacture of rolled metal products, such as steel plate, sheet, strip, rods, and bars, it has become increasingly important to maintain a high degree of uniformity in the finished product, not only as to the metallurgical properties, but also as to the dimensions of the product. Although present day continuous and semi-continuous rolling mills appear to be, and in some aspects are, highly automated, considerable reliance is placed on the skill and judgment of the operator in the pulpit and/or the operator at each stand to accurately control the production of hot and cold rolled products.

Early rolling mills included mill stands that were driven by a single motor through a gear drive. Pass reductions, individual roll diameters, and roll speeds were selected so that some degree of tension uniformity was maintained in the strip or sheet being rolled. Since all these factors were interdependent, order changes as to rolling speeds, widths, gage, and metallurgical characteristics, required the shutdown of the line for roll changes stand adjustments, and gear changes.

The more recently installed mills typically include four four-high roughing stands and six four-high finishing stands. Each stand is driven by its own variable speed DC. motor. Since the strip or sheet increases speed at each stand because of forward slip, the provision of individual stand drives simplifies the matching of mill speeds among the stands. To further simplify this matching, loopers are provided between each finishing stand to accommodate strip or sheet accmulations between the stands. The mill operator, by adjusting the roll speed of each individual stand, attempts to maintain a uniform loop length between adjacent mill stands. It will be appreciated, however, that the speed adjustment of a single stand requires the adjustment of each other mill stand, either upstream or downstream of the adjusted stand. It will be further appreciated that these adjustments require considerable skill and dexterity, particularly during overall line speed changes.

Various types of loopers are in use today. The drop looper is the most elementary form of accumulator and comprises a table or guide trough which is provided with a hinged bottom. The sheet or strip is guided between adjacent mill stands by the trough or table and, when the strip or sheet has entered the next succeeding stand, the hinged bottom is opened to permit the strip or sheet to form a catenary loop between the stands. Side loopers are employed for rods and bars and comprise a trough which directs the rod or bar to the next stand and a horizontally movable looper roller which directs the bar or rod sideways to form and maintain a horizontal loop on the mill floor. In recent years, uploopers have been provided in some mills. These uploopers usually comprise a looping roller which is mounted on a hydraulically operated arm. The arm is pivoted at one end and is moved through a plane which is vertically aligned in the rolling direction.

The loopers which are provided with looper rollers have been electrically or mechanically linked to an adjacent mill stand to control the speed of that stand in response to the loop length. Thus these loopers provide a uniform mean loop length throughout the line without manual speed adjustment of the individual stands.

The maintenance of a uniform loop length between 3,417,585 Patented Dec. 24, 1968 each stand facilitates rapid changes in over-all line speed and compensates for slight mismatching of speeds between adjacent stands. Uniformity of loop length throughout the finishing stands, however, does not by itself, contribute to uniformity of finished product characteristics such as dimensions and metallurgical properties. Uniformity as to dimensions, and particularly as to the width and gage of sheet and strip, is dependent upon the maintenance of a uniformly controlled tension along the line. Variations in tension between the rolling stands causes variations in thickness along the length of the strip. Heretofore, many loopers have been operated without regard to any variations in tension that would occur between the rolling stands. Although it has been appreciated that forward and back tension on a strip or sheet passing through a rolling stand greatly influenced the gage and the power requirements to produce that particular gage, strip or sheet tension has been tolerated only as a method of tracking the material through the stands and tension in excess of tracking tension has been avoided, probably because of its inherent lack of uniformity and inability to be controlled by the prior art looping devices.

Some loopers have been provided with linkages designed to vary the mechanical advantage of the looper actuator in such a way as to compensate for the tendency of strip tension to decrease as the loop size increases. However satisfactory and reliable loop tension control has not been fully achieved. Defiections of the linkage under load and linkage inertia may have been part of the difficulty.

The present invention provides a looping device for webs that maintains close'and reliable control of web tension despite speed and/or loop size variations.

The invention hydraulically varies the force of the looper roller on the web as a function of the configuration of the strip at the looper in such a way as to maintain, at any one of a wide range of preselected tension settings, a uniform tension of the web.

These and other objects of the invention will become apparent and more fully understood from the following detailed description of the invention, and from the accompanying drawings, in which:

FIGURE 1 is a partly schematic and partly diagrammatic illustration of a portion of a rolling mill line employing the invention; and

FIGURE 2 is a somewhat less schematic sectional view of an embodiment of part of the hydraulic looper control circuit which is illustrated schematically in FIGURE 1.

FIGURE 1 of the drawings shows a portion of the finishing line of a continuous hot strip steel mill employing a strip looper and a looper control circuit. It is to be understood, however, that the looper and its control circuit may be employed in other environments that involve the maintenance of loop control and constant strip tension during processing operations.

In FIGURE 1 the main components of the system include adjacent four-high finishing stands 10 and 11. In a typical continuous strip mill, other finishing stands are provided to progressively reduce the continuous strip as the strip passes through the working rolls at each stand. Midway between each adjacent finishing stand and, as illustrated, between the stands 10 and 11, a looper 12 is provided. The looper 12 is an uplooper and includes a looper roller 13 which is mounted in a yoke carried by a piston rod 14 which is associated with a hydraulic cylinder 15. The rod 14 reciprocates vertically.

A main drive motor 22 for the stand 11 is responsive to the vertical position of the looper roller 13, which position adds to or substracts from the speed at which motor 22 drives the rolls in the stand 11. An arm 23 is fixed to the piston rod 14 for movement therewith. A linkage means 24 is connected to the free end of the arm 23 and transmits the vertical position of the roller 13 to a main drive motor speed control device 25 through an input device 25b which is responsive to linkage means 24. The linkage means 24 and the input device 25b may comprise a rack and pinion or equivalent mechanisms for mechanically or electrically operating the control device 25 as a function of the change in loop size, that is, the change in the length of strip between the stands 10 and 11 or the change in position of the roller 13. Departures of the roller 13 from the selected normal operating' height (say 12" above the pass line) speed up or slow down the motor 25 from its non-departure speed, such speeding up or slowing down being in such a direction as to tend to restore the loop size corresponding to the selected normal operating height of the roller 13.

The present invention contemplates the provision, for any loop height within a normal operating range, of means to maintain a predetermined constant tension in the strip which is responsive to the position of the looper roller 13. The tension in the strip S is maintained constant where P=tension-establishing pressure in cylinder 15 (the amount by which the total pressure in cylinder 15 exceeds tare pressure) F=force in tension on strip S A=area of piston in cylinder 15 =elevation angle of the loop.

Of course A/2 is a constant. Therefore to maintain F at a constant value, when qb varies, the tension-establish ing pressure in the cylinder 15 should in theory be varied in direct proportion to sine 6. At angles of from zero to about six degrees, the sine is almost proportional to the angle, the proportionality holding to three and almost to four significant figures. Even at angles of from six to say ten degrees the departures from a relationship of strict proportionality are slight. Therefore at these low elevation angles if the tension-establishing pressure in the cylinder 15 is varied in proportion to the angle 95, the tension on the strip will remain constant to three or four significant figures.

Furthermore, sines and tangents of angles up to about six degrees diifer very little (they are the same to three significant figures) and differ only slightly more up to about ten degrees. Therefore at low elevation angles, the vertical height of the roller 13 is a direct measure of the angle to or almost to three significant figures, and if the tensionestablishing pressure in the cylinder 15 is varied in proportion to the height of the roller 13, the tension in the strip will be maintained constant to an accuracy almost as great as if the tension-establishing pressure were directly governed by the elevation angle.

The elevation angles should not during operation vary below say two or three or preferably four degrees, since at these very low angles the control of strip tension may not be sufiiciently definite due to the huge mechanical advantage of the upthrusting roller 13.

The maintenance of uniform loop length involves some slightly up and down movement of the length-sensing looper roller, but this need not be so great as to cause the elevation angle to vary by more than several degrees. The loop length control should be set to maintain a loop length corresponding to an elevation angle of say five or six degrees. Thus such an elevation angle of say five or six degrees will form the center of the range of several degrees through which the elevation angle varies as an incident of the up and down movement of the length-sensing looper roller as it acts as part of the loop length control. Therfore during operation the elevation angle will not vary below say two, three or four degrees.

In a rolling mill, for example, the finishing stands are usually eighteen feet apart and a loop height is preferably maintained at say about twelve inches above the pass line, making the angle roughly about six degrees. The angle preferably does not vary more than a degree or two to either side of six degrees and the calculated pressures required in the cylinder to maintain a constant strip tension for the small variations in q; are substantially the same as the straight line variations in pressure which are generated in a manner that will now be described.

A maximum pressure control valve 26 is provided and is connected to the hydraulic pressure source 17 by a conduit 27. The valve 2.6 includes housing 28 having a bore 29 therein which communicates with an enlarged chamber 30. A spool 31 is slidably mounted in the bore 29 and is provided with an area balanced recessed portion 32 which defines a chamber 33 with the bore 29. The protruding end of the spool 31 is provided with a piston 34 which is slidably mounted in a cylinder 35. Air is admitted to the cylinder 35 at a constant predetermined pressure governed by a remote adjustable pressure valve (not shown) at the pulpit. This air pressure determines strip tension. The air pressure signal is transmitted through static line 36. When the pressure in the cylinder 35 is at zero gage, the hydraulic pressure in the chamber is zero regardless of the hydraulic pressure in the chamber 33 (source pressure) since the chamber 33 is area balanced. A selected constant pressure above zero gage in the cylinder forces the spool 31 to the right and hydraulic fluid is admitted into the chamber 30. When the fluid pressure in the chamber 30 reaches a value that is sufiicient to balance the air pressure in the cylinder 35, the spool 31 shifts back to its original position closing the chamber 30. Thus the constant pressure which is maintained in the cylinder 35 establishes and maintains a constant hydraulic pressure in the chamber 30. It should be noted that the area of the piston 34 on which the air acts is large in comparison to the cross sectional area of the spool 31 upon which the hydraulic fluid in the chamber 30 acts so that relatively low pressures in the static line 36 and the cylinder 35 will balance relatively high pressures in the chamber 30. It should further be noted that selected consant air pressure values in the cylinder 35 will produce proportionate, predetermined, and constant hydraulic fluid pressures in the chamber 30.

Air pressure values in the cylinder 35 may obviously be established by means other than the static line 36 which leads from a remote valve. The pressure may be set by a local valve (not shown) which is manually adjusted or is adjusted by remote control means such as an electrical voltage or other signal which sets the local value through a suitable transducer.

The chamber 30 is connected to a ratio valve 37 by a conduit 38 which is in fluid communication with a maximum set pressure chamber 39 in the ratio valve 37. The ratio valve 37 is provided with a tare pressure chamber 40. Means are provided to maintain the hydraulic fluid in the chamber 40 at a pressure which is sufficient to support the weight of the elements of the looper 12 in an unloaded condition. To this end the chamber 40 is connected to a constant pressure outlet valve 41 by a conduit 42. The valve 41 includes a spool 43 which is loaded by a spring 44 to release fluid to a reservoir when the pressure in the chamber 40 exceeds the predetermined tare pressure. The force exerted by the spring 44 may be varied by an adjusting screw 44b to compensate for any weight changes that may be made in the looper 12, i.e. the replacement of the roller 13 with a roller of a different weight.

The control valve 26, ratio valve 37, and outlet valve 41 may all be contained in the same housing, if desired. The chambers 30 and 39 may be a single common chamber, and the valve 41 may open directly from the chamber 40.

The constant pressure in the chamber 39 should exceed the maximum pressure that is required in the cylinder to maintain the desired tension in the strip at the greatest possible loop height. Adjustment of this constant pressure will (by changing the slope of the curve which represents a plot of pressure against loop height) change the value of tension that is maintained in the strip.

The pressure in the chamber 40 is independent of any of the factors that determine the selection of the pressure in the chamber 39 but is a constant for all strip tensions. The pressure in the chamber 40 establishes the tare pres sure of the cylinder 15.

The chambers 39 and 40 are connected by bores which are enlarged to form a pressure modulating chamber 46 in the valve 37 between and in fluid communication with the chambers 39 and 40. A proportioning spool 47 is slidably mounted in the bore 45 and extends through the chamber 46 and partly into the chambers 39 and 40. The proportioning spool 47 is provided with a longitudinal slot 48. The slot 48 defines first and second orifices 49 and 50, respectively, between the chambers 39 and 46 on the one hand and between the chambers 46 and 40 on the other hand.

The spool 47 is urged toward the right, as viewed in FIGURE 1, by the relatively high fluid pressure in the chamber 39 and butts against a rod 51.

The rod 51 is slidably mounted through the housing of the valve 37 and extends into the chamber 40. The rod 51 is axially movable in either direction to urge the spool 47 to the left against the fluid pressure in the chamber 39 or permit the spool 47 to be urged to the right by the fluid pressure in the chamber 39. When the spool 47 is urged to the right or to the left from its centered position illustrated in FIG. 1, the orifices 49 and 50 open and close in inverse relationship. Thus, when the rod 5'1 moves the spool 47 to the left against the fluid pressure in the chamber 39, the orifice 49 progressively opens and the orifice 50 progressively closes. Conversely, when the rod 51 permits the spool 47 to be moved to the right by the fluid pressure in the chamber 39, the orifice 50 progressively opens and the orifice 49 progressively closes.

The above described axial movement of the rod 51 is dependent upon and responsive to the position of the arm 23 and, therefore, the height of the looper roller 13. To this end a position responsive means adjusts the position of the rod 51 in response to the position of the arm 23. This means includes the linkage 24, an input device 52, and a motion reducer 53. The linkage 24 and the input device 52 may comprise a tape and spring return reel or a rack and pinion, or other equivalent system for axially positioning the rod 51 in accordance with the vertical position of the arm 23. If the linkage 24 and the input device 52 comprise a tape and reel or other equivalent means for feeding a rotational signal into the motion reducer 53, the motion reducer 53 may comprise a reduction gear box or a screw thread for the rod 51.

In the condition shown in FIGURE 1, the orifices 49 and 50 are equal in area and the spool 47 is in a centered position. A downward movement of the looper roller 13 and its arm 23 causes the rod 51 and the spool 47 to move to the right, thus opening the orifice 50 and progressively closing the orifice 49. Conversely, an upward movement of the looper roller 13 and its arm 23 causes the rod 51 and the spool 47 to move to the left, thus opening the orifice 49 and progressively closing the orifice 50.

As was previously explained, the pressure in the chamber 39 is established and maintained at a value which is slightly in excess of the calculated maximum pressure that is required in the cylinder 15 to maintain a predetermined tension in the strip for the greatest possible loop height and the pressure in the chamber 40 is established and maintained at a value which is required in the cylinder 15 to support the looper 12 in an unloaded condition. The pressure in the chamber 40, furthermore, is a constant value. Since the pressure in the chamber 39 is always maintained at a value which is higher than the pressure in the chamber 40 and since the chambers 39, 46, and 40 are in fluid communication, a pressure drop occurs between the chambers 39 and 40. Since the pressures in the chambers 39 and 40 are maintained constant, the total pressure drop is likewise a constant.

This pressure drops occurs at the orifices 49 and 50 and varies at each orifice as an inverse function of the amount that the orifice is opened. This pressure drop between the chambers 39 and 40, therefore, produces a pressure in the chamber 46 which is a value that is less than the pressure in the chamber 39 and more than the pressure in the chamber 40 and which is a function of the position of the spool 47. This pressure is analogous to the voltage at the sliding contact of a resistance bridge.

When the looper roller 13 is in the position illustrated in FIGURE 1, the loop height is at a desired normal loop height for this device and consequently the orifices 49 and 50 may be opened in equal amounts. In the illustrated condition, the pressure in chamber 46 is onehalf of the difference in pressures between the maximum set pressure (the pressure in the chamber 39) and the tare pressure (the pressure in the chamber 40). If the looper roller 13 rises, the spool 47 moves to the left to progressively reduce the orifice 50 and increase the orifice 49. As the looper roller 13 lowers, the spool 47 is urged to the right to reduce the orifice 49 and open the orifice 50.

Theoretically, if the flow rates through the orifices 49 and 50 are very high and the changes in position of the roller 13- are sufiiciently gradual, the modulated pressure that is produced in the chamber 46 can be transmitted directly to the cylinder 15 to impart a constant tension to the strip S for any loop height, but this involves great ineificiencies in pumping losses and wasted work, or else provides a very low and generally wholly inadequate power output. Therefore, the output of the proportioning valve is utilized as a pressure signal, and the chamber 46 is connected to a power amplifier such as a collating Valve 54 which compares the pressure signal from the chamber 46 with the actual pressure in the cylinder 15 and supplies fluid to the cylinder 15 in response to pressure deficiencies in tht cylinder 15 and corrects pressure excesses that are sensed in the cylinder 15 by, respectively, connecting the cylinder 15 directly to the hydraulic pressure source 17 and porting the cylinder 15 to a reservoir.

The chamber 46 in the ratio valve 37 is connected to a chamber 55 in the collating valve 54 by a conduit 56. A second chamber 57 is provided in the valve 54 and is connected to the hydraulic cylinder 15 by a conduit 58. An area balanced spool 59 is slidably mounted in the valve 54 and separates the chambers 55 and 57. The spool 59 is slidable between stop members 60 and 61 in response to fluid pressure variations between the chambers 55 and 57 to connect an outlet port 62 to a drain conduit 63 when the pressure in the chamber 57 exceeds the pressure in the chamber 55 and to connect an inlet port 64 to the pressure source 17 through a conduit 65 when the pressure in the chamber 55 exceeds the pressure in the chamber 57. In its position illustrated in FIGURE 1, the spool 59 is in neutral position blocking both the inlet and outlet passageways 64 and 62, respectively, thus indicating equal pressures on both ends of the spool 59. Very small movements of the spool 59 to the right or left of this centered position will open either the passageway 64 to the conduit 65 or the passageway 62 to the conduit 63. Thus, during the normal operation of the looper 12, the spool 59 will rarely butt against the stop members 60 and 61 since any movement of the spool 59 tends to immediately equalize any overbalanced pressures acting on the spool 59.

When a strip is originally to be trained between the stands 10 and 11, the looper 12 is in a lowered position. This position may be established by reversing the 'valve 66 from the position shown in FIGURE 1, causing the pressure in 55 to drop to drain pressure and thereby causing cylinder 15 to be connected to drain. Just prior to this, the control is disconnected from the input 25b, and the control 25 is therefore unaware of loop length error and operates as if normal loop length were maintained.

After the strip is entrained, the valve 66 is shifted back to the operating position shown in FIGURE 1 and at the same time the control 25 is connected to the input 251) so as to again receive signals of error in loop length and correspondingly control the motor 22. These changeovers may be made by manually operated switches and valves or by automatic devices (not shown) responsive to en training or detraining of the strip through the roll stands 10 and 11.

FIGURE 2 illustrates a detailed embodiment of the ratio valve 37 shown schematically in FIGURE 1. Insofar as possible, the same numerals are employed in FIG- URE 2 that are used for describing the corresponding elements of the schematic valve of FIGURE 1, except that the numerals employed for the corresponding elements of FIGURE 2 are followed by the suifix a.

In FIGURE 2, a ratio valve 37a is illustrated. A conduit 38a connects the chamber (see FIGURE 1) to the ratio valve 37a and is in fluid communication with a maximum set pressure chamber 3%. The pressure chamber 39a is defined by a hollow plug 80 which is inserted into a bore 81 in the valve body. An axial bore 82 is drilled through one circular face of the plug 80 and the bore 82 slidably receives and supports one end of a cylindrical proportioning spool 47a.

The ratio valve 37a is provided with a tare pressure chamber 40a which is connected to the constant pressure outlet valve 41 (see FIGURE 1) by a conduit 42a. The pressure chamber 40a is defined by a hollow cylinder 83 which is inserted into the bore 81 in the valve body. An axial bore 84 is drilled through the circular face of the cylinder :83 and the bore 84 slidably receives and supports the other end of the cylindrical proportioning spool 47a.

The constant pressure in the chamber 39a should exceed the maximum pressure that is required in the cylinder 15 to maintain the desired tension in the strip for the greatest possible loop height.

The pressure in the chamber 40a is independent of any of the factors that determine the selection of the pressure in the chamber 39:: but is a constant for all strip tensions. The pressure in the chamber 40a establishes the tare pressure of the cylinder 15.

A pressure modulating chamber 46a is defined by the bore 81 and by the opposed circular faces of the cylinders 80 and 83. The modulating chamber 46a is in fluid communication with the chambers 39a and 40a through a longitudinal slot 48a which is cut into the cylindrical side wall of the spool 47a. The slot 48a defines first and second orifices 49a and 50a, respectively, between the chambers 39a and 46a on the one hand and between the chambers 46a and 49a on the other hand.

The spool 47a is urged toward the right, as viewed in FIGURE 2, by the relatively high fluid pressure in the chamber 39a and butts against a rod 510.

The rod 51a is mounted in a guide sleeve 85 and extends into the chamber 40a. The rod 51a is axially movable relative to the guide sleeve in either direction to urge the spool 47a to the left against the fluid pressure in the chamber 39a or permit the spool 47a to be urged to the 8 right by the fluid pressure in the chamber 39a. When the spool 47a is urged to the right or to the left from its centered position illustrated in FIGURE 2, the orifices 49a and 50a open and close in inverse relationship. Thus when the rod 51a moves the spool 47a to the left against the fluid pressure in the chamber 39a, the orifice 49a progressively opens and the orifice 50a progressively closes. Conversely, when the rod 51a permits the spool 47a to be moved to the right by the fluid pressure in the chamber 39a, the orifice 50a progressively opens and the orifice 49a progressively closes.

The above described axial movement of the rod 51a is dependent upon and responsive to the position of the arm 23 and, therefore, the position of the looper roller. To this end the position responsive means which is associated with the arm 23, and which has been described above, is arranged to impart a rotational movement to the free end of the rod 51a. A screw thread connection 53a is provided between the guide sleeve and the rod 51a to greatly reduce the motion of the arm 23.

In the embodiment illustrated in FIGURE 2, the orifices 49a and 50a are equal in area, and the spool 47a is in a centered position. A downward movement of the looper roller 13 and its arm 23 causes the rod 51a and the spool 47a to move to the right, thus opening the orifice 50a and progressively closing the orifice 49a. Conversely, an upward movement of the looper roller 13 and its arm 23 causes the rod 51a and the spool 47a to move to the left, thus opening the orifice 49a and progressively clos ing the orifice 50a.

Since the pressure in the chamber 39a is always maintained at a value which is higher than the pressure in the chamber 40a, and since the chambers 39a, 46a, and 40:: are in fluid communication, a pressure drop occurs between the chambers 39a and 40a. Since the pressure in the chambers 39a and 40a are maintained constant, the total pressure drop is likewise a constant.

This pressure drop occurs at the orifices 49a and 50a and varies at each orifice as an inverse function of the amount that the orifice is opened. This pressure drop between the chambers 39a and 40a, therefore, produces a pressure in the chamber 46a which is a value that is less than the pressure in the chamber 39a and more than the pressure in the chamber 40a and which is a function of the position of the spool 47a.

If the flow rates through the orifices 49a and 50a are very high, the modulated pressure that is produced in the chamber 46:: can be transmitted directly to the cylinder 15 to impart a constant tension to the strip S for any loop height. Preferably, however, the chamber 46a is connected to the collating valve 54 by a conduit 56a.

The total area of the orifices 49a and 50a may be initially adjusted by changing the position of the cylinder 83 with respect to the fixed position of the cylinder 80. This is accomplished by axially adjusting the position of the guide sleeve 85, which butts against the cylinder 83, relative to the bore 81. The projecting end of the guide sleeve 85 is provided with screw threads 86 which register with a tapped end portion 87 of the bore 81. When a desired total orifice area is achieved, the sleeve may be locked in its adjusted position by means of a set screw 88.

For purposes of this application strip is to be understood to include Wires, cords, monofilaments, and narrow tapes, as well as metal sheets, strips, bars, plates, and other elongated metal products.

It should be understood from the above that in the particular embodiment illustrated, the elements 1214 comprise a strip support means to take-up slack and form a substantially straight-sided loop in the strip S and impose tension on the strip. It will also be apparent that this strip support means is mounted for vertical translation and constitutes a vertically reciprocating linkage. Furthermore, the hydraulic control system terminating at the cylinder 15 comprises hydraulic means for generating a tension-establishing hydraulic pressure that varies substantially as the side of the angle which is formed between a straight side of the loop and a horizontal plane between the roll stands and 11 (i.e., the pass line) and for imposing such pressure on the roller through the vertically reciprocating linkage. By tension-establishing pressure is meant the total pressure in the hydraulic cylinder 15 less the tare pressure. The tare pressure is established by the setting of the valve 41 which in turn determines the pressure in the tare pressure chamber 40 and therefore determines the lower limit of the pressure potential between the chambers 39 and 40.

It should also be clear that the generating means for generating the tension-establishing pressure comprises the proportioning valve including the member 47 (or 47a) and associated elements. This member slides through a first bore formed between the high pressure chamber 39 (or 39a) and the intermediate pressure chamber 46 (or 46a) and also through a second bore formed between the intermediate pressure chamber 46 (or 46a) and the low pressure chamber or tare pressure chamber 40 (or 40a).

Thus the orifices 49 (or 49a) and 50 (or 50a) are defined by axial projections of the interfaces between the above-mentioned first and second bores and the sliding member 47 (or 47a). The orifices each have an intermediate size corresponding to the intermediate sliding position of the member 47 (or 47a), such intermediate positions being illustrated in FIGURE 1 (or FIGURE 2).

Therefore each of the orifices varies from its intermediate-position size according to its own function of the direction and amount of displacement of the sliding member 47 (or 47a) from the illustrated intermediate position. The function by which each of the orifices 49 and 50 so varies is inverse to the function by which the other of the orifices 49 and 50 so varies. The same is true of the orifices 49a and 50a.

The scope of the invention is not limited to the slavish limitation of all the structural and operative details mentioned above. These have been given merely by way of an example of a presently preferred embodiment of the invention.

What is claimed is:

1. In apparatus comprising at least one pair of adjacent strip rolling stands which have drive means for controlling the length of strip between the stands, and which have a loaded strip support means to take up slack and form a substantially straight-sided loop and impose tension on the strip, means for mounting said strip support means for vertical translation, said strip support means constituting a vetrically reciprocating linkage, hydraulic means for generating a tension-establishing hydraulic pressure that varies substantially as the sine of the angle which is formed between a straight side of the loop of the plane of the pass line between the roll stands and for imposing said pressure on said roller through said vertically reciprocating linkage, said pressure generating means comprising (1) signal generating means including valve means for producing a tensionestablishing fluid pressure signal that increases substantially instantaneously with the translational change of said strip support means and as the sine of said angle increases, and that decreases substantially instantaneously with the translational change of said strip support means and as the sine of said angle decreases, and (2) collating valve means for power amplification of said pressure signal to maintain the tensions called for by said signal during changes in roller position.

2. In apparatus comprising at least one pair of adjacent strip rolling stands which have drive means for controlling the length of strip between the stands so thereby control loop size between the stands, and which have a loaded strip support means to take up slack and form a substantially straight-sided loop and impose tension on the strip, means for mounting said strip support means for vertical translation, said strip support means constituting a vertically reciprocating linkage, hydraulic means including valve means for generating a tension-establishing hydraulic pressure that increases substantially instantaneously with the translational change of said strip support means and as the sine of the angle, which is formed between a straight side of the loop and the plane of the pass line between the roll stands, increases, and that decreases substantially instantaneously with the translational change of said strip support means and as the sine of the angle decreases, and for imposing said pressure on said roller through said vertically reciprocating linkage.

3. In apparatus comprising at least one pair of adjacent strip rolling stand-s which have drive means for controlling the length of strip between the stands to thereby control loop size between the stands, and which have a loaded strip support means to take up slack and form a substantially straight-sided loop and impose tension on the strip, means for mounting said strip support means for vertical translation, said strip support means constituting a vertically reciprocating linkage, hydraulic means for generating a tension-establishing hydraulic pressure that varies substantially as the sine of the angle which is formed between a straight side of the loop and the plane of the pass line between the roll stands and for imposing said pressure on said roller through said vertically reciprocating linkage, said pressure generating means comprising means for producing a pressure output that varies substantially as the sine of said angle, said pressure-output producing means comprising a proportioning valve having a high constant pressure chamber, an intermediate variable pressure chamber, and a low constant pressure chamber, and means for valving hydraulic fluid from the high pressure chamber successively to the intermediate pressure chamber and then to the low pressure chamber, said valving means comprising a sliding member extending from the high pressure chamber through a first bore and through the intermediate pressure chamber and through a second bore and into the low pressure chamber, said sliding member being apertured to define, at its intermediate sliding position, a first variable orifice between said high constant pressure chamber and said intermediate variable pressure chamber and a second orifice between said intermediate variable pressure chamber and said low constant pressure chamber.

4. In apparatus comprising at least one pair of adjacent strip rolling stands which have drive means for controlling the length of strip between the stands to thereby control loop size between the stands, and which have a loaded strip support means to make up slack and form a substantially straight-sided loop and impose tension on the strip, means for mounting said strip support means for vertical translation, said strip support means constituting a vertically reciprocating linkage, hydraulic means for generating a tension-establishing hydraulic pressure that Varies substantially as the sine of the angle which is formed between a straight side of the loop and the plane of the pass line between the roll stands and for imposing said pressure on said roller through said vertically reciprocating linkage, said pressure generating means comprising means for producing a pressure output that varies substantially as the sine of said angle, said pressure-output producing means comprising a proportioning valve having a high constant pressure chamber, an intermediate variable pressure chamber, and a low constant pressure chamber, and means for valving hydraulic fluid from the high pressure chamber successively to the intermediate pressure chamber and then to the low pressure chamber, said valving means comprising a sliding member extending from the high pressure chamber through a first bore and through the intermediate pressure chamber and through a second bore and into the low pressure chamber, said sliding member being apertured to define, at its intermediate sliding position, a first variable orifice between said high constant pressure chamber and said intermediate variable pressure chamber and a second orifice between said intermediate variable pressure chamber and said low constant pressure chamber, said orifices being defined at axial projections of the interfaces between said first and second bores and the sliding member, and said orifices each having an intermediate size corresponding to said intermediate sliding position, each of said orifices varying from its intermediate-position size according to its own function of the direction and amount of displacement of said sliding member from said intermediate sliding position, said functions being inverse to each other.

5. In apparatus comprising at least one pair of adjacent strip rolling stands which have drive means for controlling the length of strip between the stands to thereby control loop size between the stands, and which have a loaded strip support means to take up slack and form a substantially straight-sided loop and impose tension on the strip, means for mounting said strip support means for vertical translation, said strip support means constituting a vertically reciprocating linkage, hydraulic means for generating a tension-establishing hydraulic pressure that varies substantially as the sine of the angle which is formed between a straight side of the loop and the plane of the pass line between the roll stands and for imposing said pressure on said roller through said vertically reciprocating linkage, said pressure generating means comprising means for producing a pressure signal that varies substantially as the sine of said angle, said signal producing means comprising a proportioning valve having a high constant pressure chamber, an intermediate variable pressure chamber, and a low constant pressure chamber, and means for valving hydraulic fluid from the high pressure chamber successively to the intermediate pressure chamber and then to the low pressure chamber, said valving means comprising a sliding member extending from the high pressure chamber through a first bore and through the intermediate pressure chamber and through a second bore and into the low pressure chamber, said sliding member being apertured to de fine, at its intermediate sliding position, a first variable orifice between said high constant pressure chamber and said intermediate variable pressure chamber and a second orifice between said intermediate variable pressure chamber and said 10w constant pressure chamber, said orifices being defined at axial projections of the interfaces between said first and second bores and the sliding member, and said orifices each having an intermediate size corresponding to said intermediate sliding position, each of said orifices varying from its intermediate-position size according to its own function of the direction and amount of displacement of said sliding member from said intermediate sliding position, said functions being inverse to each other, said pressure generating means also comprising collating valve means for power amplification of said pressure signal to maintain the tensions called for by said signal during changes in roller position.

References Cited UNITED STATES PATENTS 2,221,592 11/1940 Lessmann 72238 2,921,602 1/1960 Brinkel 137625.66 2,954,801 10/1960 Nelson l37625.66 3,182,686 5/1965 Zilberfarb 137-81.5

CHARLES W. LANHAM, Primary Examiner.

K. C, DECKER, Assistant Examiner.

U.S. Cl. X.R. 72-15, 205

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,417,585 December 24, 1968 Wayne G. Ritter It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 16, "drops should read drop line 52, "tht" should read the Column 9, line 1, "side" shou read sine line 54, "of", second occurrence, should read and line 70, "so" should read to Column 10, line 49, "make" should read take Signed and sealed this 17th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

3. IN APPARATUS COMPRISING AT LEAST ONE PAIR OF ADJACENT STRIP ROLLING STANDS WHICH HAVE DRIVE MEANS FOR CONTROLLING THE LENGTH OF STRIP BETWEEN THE STANDS TO THEREBY CONTROL LOOP SIZE BETWEEN THE STANDS, AND WHICH HAVE A LOADED STRIP SUPPORT MEANS TO TAKE UP SLACK AND FORM A SUBSTANTIALLY STRAIGHT-SIDED LOOP AND IMPOSE TENSION ON THE STRIP, MEANS FOR MOUNTING SAID STIP SUPPORT MEANS FOR VERTICAL TRANSLATION, SAID STRIP SUPPORT MEANS CONSTITUTING A VERTICALLY RECIPROCATING LINKAGE, HYDRAULIC MEANS FOR GENERATING A TENSION-ESTABLISHING HYDRAULIC PRESSURE THAT VARIES SUBSTANTIALLY AS THE SINE OF THE ANGLE WHICH IS FORMED BETWEEN A STRAIGHT SIDE OF THE LOOP AND THE PLANE OF THE PASS LINE BETWEEN THE ROLL STANDS AND FOR IMPOSING SAID PRESSURE ON SAID ROLLER THROUGH SAID VERTICALLY RECIPROCATING LINKAGE, SAID PRESSURE GENERATING MEANS COMPRISING MEANS FOR PRODUCING A PRESSURE OUTPUT THAT VARIES SUBSTANTIALLY AS THE SINE OF SAID ANGLE, SAID PRESSURE-OUTPUT PRODUCING MEANS COMPRISING A PROPORTIONING VALVE HAVING A HIGH CONSTANT PRESSURE CHAMBER, AN INTERMEDIATE VARIABLE PRESSURE CHAMBER, AND A LOW CONSTANT PRESSURE CHAMBER, AND MEANS FOR VALVING HYDRAULIC FLUID FROM THE HIGH PRESSURE CHAMBER SUCCESSIVELY TO THE INTERMEDIATE PRESSURE CHAMBER AND THEN TO THE LOW PRESSURE CHAMBER, SAID VALVING MEANS COMPRISING A SLIDING MEMBER EXTENDING FROM THE HIGH PRESSURE CHAMBER THROUGH A FIRST BORE AND THROUGH THE INTERMEDIATE PRESSURE CHAMBER AND THROUGH A SECOND BORE AND INTO THE LOW PRESSURE CHAMBER, SAID 